In a hard disk drive (HDD), there are servo spokes and servo sectors in the spokes that contain servo information on the read/write (RW) head's location with respect to the spinning disk of the HDD. The information can include fields such as AGC (automatic gain control), SAM (servo address mark), Track ID (track identification), Position Error Signal (PES) bursts and other information. The servo information is critical for the drive to function properly as the RW head needs to go to each target location to read or write data, and the servo information lets the drive know that it is precisely at which location, or how much to traverse to reach the targeted location.
To generate the servo information in the servo spokes, it is necessary to first write the servo information in the form of servo patterns. For conventional HDDs, these are accomplished by a few approaches, such as Media Servo Track Writing, internal self-servo write, internal write using push-pin and in some cases, contact servo printing (CSP). The first 3 approaches (used by a majority of HDDs manufacturers) use a RW head which needs to traverse to each track to write the servo information. For dedicated servo HDDs, a wide writer approach is employed, using shingled magnetic recording approach.
However as the areal density of HDDs increase, the width of the tracks in the HDD is reduced correspondingly. This increase in track density (tracks per inch, TPI) is generally much more than the increase in linear density. When TPI increases, there are more tracks to write (for the approaches using RW head) during servo writing and the corresponding time taken to complete servo writing increases significantly and affects throughput. Accordingly, there is a problem in that an increasing TPI and reducing writer dimensions result in increased servo pattern writing time and affect throughput.
In the dedicated servo approach, the servo layer is positioned below the data layer. The servo writing problem is made more challenging due to the need to write to the separate servo layer. It is harder to write servo pattern on this dedicated servo layer using a conventional head based approach because of the following. The larger head media spacing (HMS) makes the servo layer harder to write by a conventional RW head due to insufficient write field. Further, the larger head media spacing (HMS) makes it difficult for the servo layer to be written by conventional means (using flying head) while achieving very high resolution and good track pitch. In addition, the magnetic properties of the servo layer need to become higher as that of the data layer increases to support higher areal density, and this also makes the requirements higher on a suitable RW head for servo writing. For example, there may be need for the servo layer ku (magnetic anisotropy constant) and He (coercivity) to become higher in relation to the higher ku and He of the data layer. Further, the dimension of the writer on the slider is getting smaller (longer servo write time) and the achievable write field is becoming less.
Thus, there is need for an approach to write servo patterns that may address the above-mentioned issues, including for example a fast method to create one or more servo patterns on (conventional) disks.